Hybrid full duplex communications in a radio frequency cable network

ABSTRACT

Systems and methods presented herein provide for improved duplex communications in an RF cable network comprising a plurality of CMs. In one embodiment, a system includes a CMTS operable to transmit downstream communications to the CMs and to process upstream communications from the CMs. The system also includes a duplex RF communication path between the CMTS and the CMs. The CMTS is further operable to transmit a control signal that directs a first of the CMs to transmit, to direct the remaining CMs to receive the transmission from the first CM, to direct the CMs to report received power levels of the transmission from the first CM, and to calculate RF isolations of the remaining CMs with respect to the first CM based on the reported power levels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.15/700,951, filed Sep. 11, 2017, which prior application was acontinuation of U.S. application Ser. No. 15/019,686, filed Feb. 9,2016, now U.S. Pat. No. 9,762,377, which application claims the benefitof U.S. provisional Application No. 62/234,085, filed Sep. 29, 2015, thedisclosures of which are incorporated in their entirety by referenceherein.

BACKGROUND

A duplex communication system is a point-to-point system composed of twoconnected parties or devices that can communicate with one another inboth directions. Generally, a duplex system has two clearly defined datatransmission channels, with each channel carrying information in onedirection. In a full duplex system, both parties/devices can communicatewith each other simultaneously using the same physical spectrumchannels.

In a (Radio Frequency) RF cable network, full duplex communications canbe more difficult to achieve due to the number of “downstream” devicesand the network configuration. For example, a Cable Modem TerminationSystem (CMTS) is typically coupled to a plurality of downstream CableModems (CMs). Each of the CMs can transmit “upstream” along the samepath to the CMTS while the CMTS transmits its downstream communicationsto the CMs. The CMs and the CMTS generally use different spectral bands.The CMs can also transmit at specific coordinated times. However,because many CMs are transmitting to the CMTS, they tend to interferewith one another as well as with the CMTS if they are not separated intime and spectrum bands, as required in Frequency Division Duplex (FDD),Time Division Multiple Access (TDMA), and Time Division Duplex methodscurrently practiced.

SUMMARY

Systems and methods presented herein provide for improved duplexcommunications in an RF cable network. The embodiments herein illustratehow upstream and downstream transmissions can be received correctly inthe presence of one another and in the same spectrum channels. Fullduplex communication is achieved over the channel while creating fullduplex functionality in a single device, rather than requiring alldevices support full duplex functionality and associated interferencecancellation. The impact of upstream transmission from the CMs ondownstream transmission is mitigated so as to ensure that the downstreamtransmissions to the CMs are received correctly, and vice versa.

In one embodiment, a system is operable in a Radio Frequency (RF) cablenetwork comprising a plurality of CMs. The system includes a CMTSoperable to transmit downstream communications to the CMs and to processupstream communications from the CMs. The system also includes a duplexRF communication path between the CMTS and the CMs. The CMTS is furtheroperable to transmit a control signal that directs a first of the CMs totransmit, to direct the remaining CMs to receive the transmission fromthe first CM, to direct the CMs to report received power levels of thetransmission from the first CM, and to calculate RF isolations of theremaining CMs with respect to the first CM based on the reported powerlevels.

The various embodiments disclosed herein may be implemented in a varietyof ways as a matter of design choice. For example, some embodimentsherein are implemented in hardware whereas other embodiments may includeprocesses that are operable to implement and/or operate the hardware.Other exemplary embodiments, including software and firmware, aredescribed below.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the present invention are now described, by way ofexample only, and with reference to the accompanying drawings. The samereference number represents the same element or the same type of elementon all drawings.

FIG. 1 is a block diagram of an exemplary communication system in an RFcable network.

FIG. 2 is a flowchart of an exemplary process of the communicationsystem of FIG. 1.

FIG. 3 is a flowchart of another exemplary process of the communicationsystem of FIG. 1.

FIG. 4 is a flowchart of another exemplary process of the communicationsystem of FIG. 1.

FIG. 5 illustrates an exemplary ranging probe used to generate a gap intime in the downstream channels.

FIG. 6 illustrates exemplary band specific upstream probes matched todownstream frequency gap.

FIG. 7 illustrates exemplary spectrum gaps as a function of time.

FIG. 8 illustrates an exemplary frequency allocation duringinitialization and low traffic periods.

FIG. 9 illustrates exemplary upstream probes superimposed in time andfrequency to downstream 50 KHz scattered pilot signals.

FIG. 10 illustrates exemplary upstream probes of 25 KHz subcarrierspaced downstream and upstream channels superimposed in time andfrequency to a downstream channel, wherein the upstream probes of a CMcoincide with the downstream pilots.

FIGS. 11A-11B are block diagrams of exemplary four way tap designsutilizing attenuation at drop ports to increase isolation.

FIGS. 12A-12D illustrate exemplary variable upstream and downstreambandwidths switchable to half-duplex or full-duplex operation.

FIG. 13 is a block diagram of the exemplary communication system of FIG.1 employing an interference canceller.

FIG. 14 is a block diagram of an exemplary interference cancellerconfigured with a CMTS.

FIG. 15 is a block diagram of an exemplary interference cancellerconfigured with a CM.

FIG. 16 is a block diagram of an exemplary communication system in whichthe embodiments herein may operate.

FIG. 17 is a block diagram of an exemplary computing system in which acomputer readable medium provides instructions for performing methodsherein.

DETAILED DESCRIPTION OF THE FIGURES

The figures and the following description illustrate specific exemplaryembodiments of the invention. It will thus be appreciated that thoseskilled in the art will be able to devise various arrangements that,although not explicitly described or shown herein, embody the principlesof the invention and are included within the scope of the invention.Furthermore, any examples described herein are intended to aid inunderstanding the principles of the invention and are to be construed asbeing without limitation to such specifically recited examples andconditions. As a result, the invention is not limited to the specificembodiments or examples described below.

FIG. 1 is a block diagram of an exemplary communication system 10 in anRF cable network. The communication system 10 includes a CMTS 11 and aplurality CMs 12-1-12-N (where “N” represents an integer greater than“1” and not necessarily equal to any other “N” reference designatedherein). The CMTS 11 is communicatively coupled to the CMs 12 through aduplex communication link 15. Generally, the CMTS 11 is coupled to theCMs 12 via a node 13 that combines the upstream communications of theCMs 12 to the CMTS 11. The CMTS 11 also provides downstreamcommunications to the CMs 12 through the duplex communication link 15.

The CMTS 11 is any system, device, software, or combination thereof,typically located in a cable company's hub site, or “headend”, which isused to provide high speed data services (i.e., the downstreamtransmissions), such as cable Internet and Voice over Internet Protocol,to the CMs 12. The CMs 12 are generally network bridges and modems thatprovides bi-directional data communication via radio frequency channelson a Hybrid Fiber-Coaxial (HFC) or Radio Frequency over Glass (RFoG).The CMs 12 are used to deliver broadband Internet access in the form ofcable Internet, taking advantage of the high bandwidth of a HFC and RFoGnetwork.

The CMTS 11 is operable to configure the CMs 12 to communicate via cableprotocol (e.g., Data Over Cable Service Interface Specification, or“DOCSIS”) specification. In this regard, the CMTS 11 is operable to sendcontrol signals that direct the CMs 12 to operate in a particular mannerwith respect to the employed cable protocol. In one embodiment, the CMTS11 is operable to calibrate the CMs 12 and periodically determinecertain characteristics of the CMs 12. For example, the CMTS 11 may senda control signal to each of the CMs 12 to determine their RF isolationswith respect to the CMTS 11 as well as their RF isolations with respectto one another. CMs 12 having greater RF isolations are less likely tointerfere with one another during duplex transmissions with the CMTS 11,thereby improving duplex communications between the CMTS 11 and the CMs12.

To illustrate, full duplex transmission is achieved by having the CMstransmit to the CMTS 11 at the same time the CMTS 11 is transmitting tothe CMs 12 using the same bands. The embodiments herein describe how theupstream/downstream transmissions can be received correctly in thepresence of other upstream/downstream transmissions. In one embodiment,a hybrid full duplex communications are achieved while creating fullduplex functionality in a single device (i.e., a CM 12), rather thanhaving all of the CMs 12 support full duplex functionality.

For downstream transmissions to be received correctly by the CMs 12, theimpact of the upstream transmissions from the CMs 12 on the downstreamtransmission from the CMTS 11 are mitigated by utilizing inherent CM toCM isolation in the communication system 10. The CMTS 11 uses knowledgeof the RF isolations between various devices (e.g., the CMs 12) andperforms CM transmission scheduling such that if a CM 12 is receiving adownstream transmission, then the CMTS 11 allows transmission for CMs 12that have an acceptable RF isolation (e.g., a threshold RF isolation)between them. Additional operational details regarding the communicationsystem 10 are shown and described in the flowchart of FIG. 2.

In FIG. 2, the process 100 initiates when the CMTS 11 transmits acontrol signal that directs a CM 12 to transmit, in the process element101. The CMTS 11 then directs the remaining CMs 12 coupled to the node13 to receive the transmission from the CM 12, in the process element102. For example, the CMTS 11 transmits a control signal to the CM 12-1that directs the CM 12-1 to begin transmitting. Then the CMTS 11transmit control signals to the remaining CMs 12-2-12-N to direct theCMs 12-2-12-N to receive the transmission from CM 12-1.

The CMTS 11 then directs the CMs 12-2-12-N to report to receive powerlevels of the transmission from the CM 12-1, in the process element 103.Based on this, the CMTS 11 calculates the RF isolations of the remainingCMs 12-2-12-N with respect the transmitting CM 12-1, in the processelement 104. The CMTS 11 then determines whether all of the RFisolations have been calculated for the CMs 12, in the process 105. Ifso, then the CMTS 11 commences duplex communications with the CMs 12having the acceptable RF isolation, in the process element 107.Otherwise, the CMTS 11 contacts the next CM 12 in the group connected tothe node 13, in the process element 106. The CMTS 11 continues theprocess until each of the RF isolations of the CMs 12 have beencalculated (e.g., by returning to the process element 101).

The CMTS 11 manages a list of the CMs 12 and their RF isolations so asto choose which CMs 12 may perform full-duplex communications with theCMTS 11. CMs not meeting the threshold level of RF isolation aredirected by the CMTS 11 to operate in a time shared and/or frequencyshared simplex operation. To illustrate, assume that the CMTS 11 hasdetermined RF isolations for a group of six CMs 12 that are connected tothe node 13. The CMTS 11 after performing the process 200 determinesthat RF isolations of the other CMs 12 with respect to the CM12-1 are asfollows

CM 12-2: RF isolation equals 74 dB

CM 12-3: RF isolation equals 66 dB

CM 12-4: RF isolation equals 45 dB

CM 12-5: RF isolation equals 70 dB

CM 12-6: RF isolation equals 73 dB

Now assume that the threshold RF isolation between the CMs 12-1-12-6operating in full-duplex mode is 62 dB. Then, when CM 12-1 is receivingdata from the CMTS 11, any of CM 12-2, CM 12-3, CM 12-5, and CM 12-6 areallowed to transmit. However, the CM 12-4 is not allowed to transmit, asany transmission from that device could adversely impact the downstreamsignal being received by CM 12-1.

Generally, the threshold value of RF isolation for concurrent operationis left to the network operator to decide based on transmissioncharacteristics and channel conditions. The threshold value can be aglobal value applicable to all of the CMs 12, or it can be defined withmore granularity for various subsets and combinations of devices.

FIG. 3 is a flowchart of another exemplary process 200 of thecommunication system 10 of FIG. 1. In this embodiment, the CMTS 11establishes a threshold RF isolation for the CMs 12 to operate infull-duplex mode, in the process element 204. As with the process 100 ofFIG. 2, the CMTS 11 determines a device to device RF isolation, in theprocess element 205. That is, the CMTS 11 determines the RF isolationsbetween each of the CMs 12-1-12-N coupled to the node 13.

The CMTS 11 may also determine which of the CMs 12 are to receivedownstream traffic from the CMTS 11, in the process element 202, anddetermine which of the CMs 12 have upstream traffic intended for theCMTS 11, in the process element 203. With these inputs, the CMTS 11 maythen perform a device pairing for each CM 12 receiving downstreamtraffic and transmitting upstream traffic while meeting the thresholdlevel of RF isolation, in the process element 201.

Once the device pairing is completed, the CMTS 11 then assigns devicepairs for downstream and upstream transmissions across various frequencybands in the duplex communication link 15, in the process element 206.For the remaining unpaired CMs 12, the CMTS assigns them to “non-full”duplex transmissions, in the process element 207. For example, the CMs12 may be directed to perform simplex communications on a time sharedand/or frequency shared basis. The CMTS 11 then generates a schedulingmatrix that directs the CMs 12 to communicate accordingly (i.e., eitheras full-duplex or non-full-duplex), in the process element 208.Thereafter, communications between the CMTS 11 and the CMs 12 aretransmitted and received, in the process element 209.

FIG. 4 is a flowchart of another exemplary process 300 of thecommunication system 10 of FIG. 1. In this embodiment, the CMTS 11receives a list of devices (e.g., CMs 12) that meet the threshold RFisolation with respect to each other, in the process element 301. TheCMTS 11 then generates a measurement matrix for transmitting andreceiving to/from the CMs 12, in the process element 302. That is, theCMTS 11 generates a matrix that determines which of the CMs 12 meet therequisite RF isolation for commencing full-duplex operations. Then, theCMTS 11 selects a group of CMs 12, in the process element 303, tocommence full duplex transmission and reception with the CMs 12.

Periodically (e.g., during low traffic periods), the CMTS 11 starts themeasurement sequence again, in the process element 304, to re-verify theRF isolations of the CMs 12, in the process element 304. In this regard,the CMTS 11 directs the CMs 12 to transmit to the CMTS 11, in theprocess element 305, such that the CMs 12 can report their transmitpower levels across the frequency bands of the duplex communication link15, in the process element 306. Similarly, the CMTS 11 will direct theCMs 12 to determine the received power levels across the frequency bandsof the duplex communication link 15 and report those power levels to theCMTS 11, in the process elements 307 and 308.

The CMTS 11 collects this data, in the process element 309, and for eachof the CMs 12, the CMTS 11 calculates the RF isolation between each ofthe CMs 12 based on the transmit and receive power levels across thefrequency bands of the duplex communication link 15, in the processelement 310. If there are remaining RF isolation measurements to be made(process element 311), then the CMTS 11 continues measuring the RFisolations of any remaining CMs 12 connected to the node 13. Otherwise,the process ends in the process element 312 and the CMTS 11 commencescommunications with the CMs 12.

FIG. 5 illustrates exemplary ranging probes 351 used to generate a gapin time in the downstream channels for training and calibrationpurposes. For example, the plot 350 illustrates upstream subcarriers andsending frequency versus data symbols being transmitted by thesubcarriers. Ranging probes 351 may be implemented during the symboltransmissions to direct the CMs 12 to initiate training and calibration.This training calibration process may be used to direct the CMs 12 toimplement their RF isolation measurement processes described above.

During this training calibration, the CMTS 11 schedules an upstreamquiet period so that a downstream probe signal 351 transmitted can beheard by its own upstream receiver. This downstream probe signal 351 maybe utilized to determine the distortion of signal received by the CMTS11 such that interference cancellation may be implemented and optimized.To generate a quiet period, the CMTS 11 may schedule a transmission of aranging probe 351 to the Null SID (Service ID). In such an embodiment,the CMs 12 are not assigned the Null SID and a transmission resulting ina gap in energy during that period does not occur.

During the quiet period, the CMTS 11 transmits downstream and listens atthe upstream receive port for upstream communications by the CMs 12. TheCMTS 11 then compares the downstream transmitted signal with thedownstream received signal at the upstream receive port. The CMTS 11then determines a transfer function H(f) in the transmission path. Alongwith the transmitted signal, an opposing transmit signal (e.g., 180° outof phase) Tx is generated for signal cancellation purposes.

Once the CMTS 11 determines the transfer function H(f), the transferfunction is represented as a digital filter G(f). The CMTS 11 thenutilizes the digital filter G(f) to modify the negated downstreamtransmit signal and creates a signal that can cancel the downstreamtransmit signal. This process may occur periodically in response tochanges in the network.

FIG. 6 illustrates exemplary band specific upstream probes 351 matchedto downstream spectrum gap 361. At the CM 12, the training process issomewhat more elaborate. For example, a partially intrusive trainingprocess may be utilized to achieve a steady state in the CMs 12. In thisapproach, the CMTS 11 generates excluded sub-bands 360, which results inone or more spectrum gaps 361 at the sub-band frequencies during periodsdetermined by the CMTS 11. At these spectrum gaps 361, the CMTS 11commands different CMs 12 to transmit a probe 351.

Even though the CMTS 11 has generated an spectrum gap 361, a CM 12 willlisten in that spectrum gap 361 on the CM 12's downstream port for theprobe 351 transmitted by the CM 12. These new band specific probes 351provide for a full duplex DOCSIS implementation that is more efficientand limits interference.

FIG. 7 illustrates exemplary spectrum gaps 361 as a function of time. Inthis embodiment, the CMTS 11 schedules the spectrum gaps 361. The CMTS11 shifts the frequency of the exclusion band as a function of timeuntil the exclusion band has stepped through the entire spectrum. Tofacilitate the calibration process for the CMs 12, the CMTS 11 transmitsdata instructing the CMs 12 when the calibration process begins, theduration of the gaps in time (e.g., as in symbols), frequencies of thegaps 361, frequency widths of the gaps 361, and when the bandgapscanning phase concludes. This is generally a dynamic process thatallows for cable plant (e.g., headend/hub) variability capable ofimpacting calibration parameters. This scanning phase process may repeatperiodically.

FIG. 8 illustrates an exemplary frequency allocation duringinitialization and low traffic periods. For example, some training andcalibration mechanisms leverage a brief period of simplex operation. Inone channel, either downstream or upstream transmissions can occur, butnot both at the same time. These periods may take place during aninitialization or when in steady state during a low traffic period. Forcalibration of the CMTS 11, the CMTS 11 can schedule quiet periods andsense the impact of downstream transmission at an upstream receive port.During period 365, the CMTS 11 transmits a downstream low frequencysignal that is received in the upstream port at the CMTS 11 to estimatelow frequency transfer function. The CM 12 transmits an upstream highfrequency signal that is received in the downstream port at the CM 12 toestimate high frequency transfer function of the CM 12. During period366, the CMTS 11 transmits a downstream high frequency signal that isreceived in the upstream port at the CMTS 11 to estimate the highfrequency transfer function of the CMTS 11. The CM 12 transmits anupstream low frequency signal that is received in the downstream port atthe CM 12 to estimate low frequency transfer function of the CM 12. Thiscompletes the low and high transfer functions at the CMTS 11 and the CM12 to assist in interference cancellation such that full duplexcommunications can occur in period 367.

In order to facilitate time coordination, the same cyclic prefix andsubcarrier spacing may be selected in the upstream and downstreamtransmissions. Since the downstream and upstream transmissions occupythe same spectrum in Full Duplex (FD), the cyclic prefix and windowingparameters defined in FD-DOCSIS can be the same for the upstream anddownstream transmissions as a superset of the DOCSIS 3.1 upstream anddownstream cyclic prefix and windowing parameters.

FIG. 9 illustrates exemplary upstream probes 351 superimposed in timeand frequency to downstream 50 KHz scattered pilot signals. FIG. 10illustrates exemplary upstream probes 370 of 25 KHz subcarrier spaceddownstream and upstream channels superimposed in time and frequency to adownstream channel, wherein the upstream probes 370 of a CM 12 coincidewith the downstream pilots. No probes are asserted during thetransmission of the Physical-layer Link Channel (PLC) 390.

In this embodiment, an alternate upstream probe is used to facilitatetraining when the probe 351 of a CM 12 coincides with a portion of thedownstream scattered or staggered pilot signals. For example, in DOCSIS3.1, the staggered downstream pilot location is based on whether thesubcarrier spacing is 25 KHz or 50 KHz. If the subcarrier spacing is 50KHz (downstream 4 KHz Fast Fourier Transform—“FFT”), the staggeringchanges by one subcarrier for every symbol that changes in time. In thecase of a 25 KHz downstream 8K FFT configuration, the subcarrierposition of the pilot signal increases by two subcarriers for everysymbol that changes in time, as shown in FIG. 10. In order to haveupstream probes achieve a superposition in time and frequency, theprobes 351 follow the behavior of the pilot signals during the period inwhich they overlap. The upstream probes 370 are then configured totraverse subcarriers to match the downstream pilot signals.

In full duplex operation there may also be interference issues when twoor more neighboring CMs 12 interfere with each other. Such may be thecase when there is poor RF isolation between CMs 12 (e.g., when CMs 12share the same tap). When two CMs 12 are connected to one or more dropcables from the same tap, there is a higher likelihood of interference.These (and other) CMs 12 may have high error rates due to interference.After switching the CMs 12 to a legacy simplex mode, these CMs 12 may beanalyzed to determine if the CMs 12 share a tap and/or if they have ahigh likelihood of interfering with one other. When there isinterference, these interfering devices may be grouped into“interference groups.”

CMs 12 in the same interference group are isolated from each other viascheduling. For example, a CM12 in an interference group will not bescheduled to transmit upstream data at the same time downstream data isscheduled to be received by another CM 12 in the same interferencegroup. Additionally, when the CMTS 11 is sending and/or broadcastingadministration messages pertaining to the CMs 12 in an interferencegroup, no upstream data is scheduled for transmission from any member ofthe interference group. It should be noted that the CMTS 11 does notschedule upstream transmissions over spectrum occupied by the PLCchannel 390.

To assist in RF isolation, tap designs can be reconfigured. FIGS.11A-11B are block diagrams of exemplary four way tap designs attenuatingat drop ports 401-404 to increase RF isolation. For example, FIG. 11Aillustrates one 4 way tap 400 where downstream signals are split off toports 401-404 using RF couplers 410. FIG. 11B illustrates analternative, more serial approach to implementing the 4 way tap. Thisalternative approach improves RF isolation by reducing the splittingthat takes place inside the tap 400 from cascading couplers instead offollowing couplers 410 by a splitter. Other tap designs (e.g., 2 way, 8way, etc.) may be used and implemented in similar fashion.

Lower tap values may further improve the RF isolation. For example,lower tap values have lower RF isolation performance than the higher tapvalues. If minimum tap values of 14 dB, 17 dB and 20 dB are used for 2,4 and 8 way taps, respectively, the minimum RF isolation would beincrease and the maximum insertion loss would decrease.

The full duplex system may be formed with network nodes each configuredwith a PHY cancellation enhancement sub-system and a digitalself-cancellation sub-system. The PHY cancellation enhancementsub-system produces the first order cancellation while the second phasecancellation further removes the effect of the transmit signal such thatthe receive signal can be recovered while the transmit signal is on.

FIGS. 12A-12D illustrate exemplary variable upstream and downstreambandwidths switchable to half-duplex or full-duplex operation. Forexample, a half-duplex or a full-duplex system may not operate inhalf-duplex or full-duplex mode unless the spectrum is available. InFIG. 12A, the RF communication link 15 may be configured so as toseparate upstream transmissions 350 from downstream transmissions 360.This link may also include an unused portion 355 of the spectrum. Theupstream transmissions 350 and the downstream transmissions 360 arevariable across the spectrum. As spectrum is needed, the upstreamtransmission 350 and downstream transmission 360 portions are pushedinto the unused portion 355, as illustrated in FIG. 12B, until there isno more unused portion of spectrum, as illustrated in FIG. 12C. But theupstream transmissions 350 and the downstream transmissions 360 arestill separate. If the system requires additional spectrum the CMTS 11can direct the CMs 12 to switch to half or full duplex as illustrated inFIG. 12D.

The embodiments herein provide full duplex communications over a channelwhile creating full duplex functionality in a single device, rather thanrequiring all devices support full duplex functionality and associatedinterference cancellation. In one embodiment, simultaneous transmissionand reception of data is assisted through the use of signalcancellation. For example, a transmitting device may improve receptionof a received signal by canceling the transmitted signal at thetransmitting device's receive port. Thus, an interference canceller canbe configured at the receive port of the CMTS 11 to cancel out thedownstream communications of the CMTS 11 from the upstreamcommunications received from the CMs 12.

FIGS. 13 and 14 are block diagrams of the communication system 10 ofFIG. 1 employing an exemplary interference canceller 20 at the CMTS 11.FIG. 15 is a block diagram of the interference canceler 20 configured atthe CM 12. In these embodiments, the interference canceler 20 removesthe transmitted signal from the received signal to improve duplexcommunications at the CMTS 11 and the CMs 12.

The interference canceler 20 generates a cancellation signal thatopposes the intended transmitted signal in both magnitude in phase. Forexample, at any single instant of time, the energy of each frequencycomponent at a receive port has a magnitude and phase. The transmittingdevice may generate a cancellation signal that has the same magnitudewith a phase that differs by 180° out of phase from the transmittedsignal to cancel the transmitted signal at the receive port. Generally,a wideband system generates a magnitude and phase from a single symbolwhile a multicarrier system has a magnitude and phase that results fromthe aggregation of the magnitudes and phases of each of its carriercomponents.

In one embodiment, before the CMTS 11's downstream transmit signalreaches the CMTS 11's upstream receive port, it traverses a PHYcancellation component. The impact of this component in addition to theeffects of other components down the network path, modify thecharacteristics of the downstream signal. This modified transmitdownstream signal cancels the downstream signal at the receive port suchthat the transmit downstream signal does not interfere with the CMTS 11reception of signals originating from other network elements (e.g., theCMs 12).

To generate the cancellation signal, the CMTS 11 may employ a digitaldistortion filter G(f). A transfer function H(f) 21 applies acancellation signal at the upstream receive port of the CMTS 11. In oneembodiment, the transfer function H(f) 21 is determined by means of atraining/calibration process. To illustrate, Tx*H(f) generates amodified downstream signal that leaks into the upstream receive port ofthe cancellation module of the CMTS 11 (where Tx′ is the 180° out ofphase cancellation signal). The transfer function G(f) is a digitallygenerated distortion function that emulates the measured distortion anddelay of the transfer function H(f)., The received signal Rx at the CMTS11 is Tx*H(f)+(Tx)′*G(f)+Rx′. Assuming ideal generation of the negateddownstream signal and an accurate representation of the distortion thedownstream signal by G(f), this yields Tx*H(f)=−(Tx)′*G(f). Theresulting signal at the CMTS 11 thus becomes Rx=Rx′.

The signal cancellation can also be employed at the CMs 12 to canceltheir upstream signals from their received ports, as illustrated in FIG.15. The interference cancellers 20 can be implemented in a variety ofways as a matter of design choice. For example, the interferencecancellers 20 can be implemented as PHY cancellation circuits using RFcirculators, splitters, transformers, couplers, and the like to extractthe signal for which cancellation is desired.

FIG. 16 is a block diagram of an exemplary communication system 800 inwhich the embodiments herein may operate. In this embodiment, thecommunication system is a cable television communication systememploying an upstream link with high speed data services being deliveredover devices conforming to the DOCSIS specification. The communicationsystem includes a headend 801 configured with an upstream hub 820. Thehub 820 is coupled to a fiber node 821 via optical communication links805 and 806. The hub 820 includes a Cable Modem Termination System(CMTS) 802 (e.g., CMTS 11 of FIG. 1), an electrical to optical converter803, and an optical to electrical converter 804. The node 821 issimilarly configured with an optical to electrical converter 808 and anelectrical to optical converter 807.

The headend 801 is the source for various television signals. Antennasmay receive television signals that are converted as necessary andtransmitted over fiber optic cables 805 to the hub 820. Several hubs maybe connected to a single headend 801 and the hub 820 may be connected toseveral nodes 821 by fiber optic cable links 805 and 806. The CMTS 802may be configured in the headend 801 or in the hub 820.

Downstream, in homes/businesses are devices and data terminals such asthe CMs 12 of FIG. 1 (not shown). The CM acts as a host for an InternetProtocol (IP) device such as personal computer. Transmissions from theCMTS 802 to the CM are carried over the downstream portion of the cabletelevision communication system generally in the band between 54 and 860MHz. Downstream digital transmissions are continuous and are typicallymonitored by many CMs. Upstream transmissions from the CMs to the CMTS802 are typically carried in the 5-42 MHz frequency band, the upstreambandwidth being shared by the CMs that are on-line. However, withgreater demands for data, additional frequency bands and bandwidths arecontinuously being deployed in the downstream and upstream paths.

The CMTS 802 connects the local CM network to the Internet backbone. TheCMTS 802 connects to the downstream path through an electrical tooptical converter 804 that is connected to the fiber optic cable 806,which in turn, is connected to an optical to electrical converter 808 atthe node 821. The signal is transmitted to a diplexer 809 that combinesthe upstream and downstream signals onto a single cable. The diplexer809 allows the different frequency bands to be combined onto the samecable. The downstream channel width in the United States is generally 6megahertz with the downstream signals being transmitted in the 54 to 860MHz band. Upstream signals are presently transmitted between 5 and 42MHz, but again other bands are being considered to provide increasedcapacity.

After the downstream signal leaves the node 821, the signal is typicallycarried by a coaxial cable 830. At various stages, a power inserter 810may be used to power the coaxial line equipment, such as amplifiers orother equipment. The signal may be split with a splitter 811 to branchthe signal. Further, at various locations, bi-directional amplifiers 812may boost and even split the signal. Taps 813 along branches provideconnections to subscriber's homes 814 and businesses.

Upstream transmissions from subscribers to the hub 820/headend 801 occurby passing through the same coaxial cable 830 as the downstream signals,in the opposite direction on a different frequency band. The upstreamsignals are sent typically utilizing Quadrature Amplitude Modulation(QAM) with forward error correction. The upstream signals can employQPSK or any level of QAM, including 8 QAM, 32 QAM, 64 QAM, 128 QAM, and256 QAM. Modulation techniques such as Synchronous Code DivisionMultiple Access (S-CDMA) and Orthogonal Frequency Division MultipleAccess (OFDMA) can also be used. Of course, any type of modulationtechnique can be used, as desired. In DOSCIS 3.1, OFDM modulation willbe used on the downstream band of the coaxial cable and OFDMA will beused on the upstream band of the coaxial cable.

Upstream transmissions, in this embodiment, are typically sent in afrequency/time division multiplexing access (FDMA/TDMA) scheme, asspecified in the DOCSIS standards. The diplexer 809 splits the lowerfrequency signals from the higher frequency signals so that the lowerfrequency, upstream signals can be applied to the electrical to opticalconverter 807 in the upstream path. The electrical to optical converter807 converts the upstream electrical signals to light waves which aresent through fiber optic cable 805 and received by optical to electricalconverter 803 in the node 820. The fiber optic links 805 and 806 aretypically driven by laser diodes, such as Fabry Perot and distributedfeedback laser diodes.

The embodiments herein may be implemented in a variety of ways as amatter of design choice. For example software and processors performingCMTS functions could be configured in a hub or a headend facility, andthe physical layer functions could be in programmable hardware in thenode. In this regard, the invention can take the form of an entirelyhardware embodiment, an entirely software embodiment or an embodimentcontaining both hardware and software elements. In one embodiment, theinvention is implemented in software, which includes but is not limitedto firmware, resident software, microcode, etc. FIG. 17 illustrates acomputing system 900 in which a computer readable medium 906 may provideinstructions for performing any of the methods disclosed herein.

Furthermore, the invention can take the form of a computer programproduct accessible from the computer readable medium 906 providingprogram code for use by or in connection with a computer or anyinstruction execution system. For the purposes of this description, thecomputer readable medium 906 can be any apparatus that can tangiblystore the program for use by or in connection with the instructionexecution system, apparatus, or device, including the computer system900.

The medium 906 can be any tangible electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system (or apparatus ordevice). Examples of a computer readable medium 906 include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Some examples of optical disksinclude compact disk-read only memory (CD-ROM), compact disk-read/write(CD-R/W) and DVD.

The computing system 900, suitable for storing and/or executing programcode, can include one or more processors 902 coupled directly orindirectly to memory 908 through a system bus 910. The memory 908 caninclude local memory employed during actual execution of the programcode, bulk storage, and cache memories which provide temporary storageof at least some program code in order to reduce the number of timescode is retrieved from bulk storage during execution. Input/output orI/O devices 904 (including but not limited to keyboards, displays,pointing devices, etc.) can be coupled to the system either directly orthrough intervening I/O controllers. Network adapters may also becoupled to the system to enable the computing system 900 to becomecoupled to other data processing systems, such as through host systemsinterfaces 912, or remote printers or storage devices throughintervening private or public networks. Modems, cable modem and Ethernetcards are just a few of the currently available types of networkadapters.

What is claimed is:
 1. A method operating a cable modem terminationsystem (CMTS) in operable communication with a plurality of cable modems(CMs) over a duplex radio frequency (RF) communication path, the methodcomprising the steps of: generating a measurement matrix of theplurality of CMs meeting a threshold RF isolation value with respect toother CMs in the plurality of CMs; determining, from the measurementmatrix, which of the plurality of CMs meet a requisite RF isolationvalue for full duplex operation; selecting a CM a measurement group,based on the step of determining, of CMs from the plurality of CMs; andcommencing full duplex transmission and reception with at least one CMof the measurement group.
 2. The method of claim 1, wherein the step ofcommencing comprises a measurement sequence of the at least one CM. 3.The method of claim 2, wherein the measurement sequence is repeated tore-verify the RF isolation of the at least one CM.
 4. The method ofclaim 2, wherein the measurement sequence is is performed in a processelement of the CMTS.
 5. The method of claim 4, further comprising a stepof receiving, from the at least one CM over the RF communication path, apower level of the at least one CM.
 6. The method of claim 5, furthercomprising a step of directing the at least one CM to report thereceived power level power level.
 7. The method of claim 5, furthercomprising a step of collecting power level data from each CM of theplurality of CMs.
 8. The method of claim 7, further comprising a step ofcalculating an RF isolation value between each of the plurality of CMs.